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X-ray nanocrystallography captures 3D images of biomolecules

How to shoot 3D movies of biomolecules at atomic resolution

July 27, 2012

Linac Coherence Light Source (credit: SLAC)

By outrunning a X-ray laser’s path of destruction, an international research team has created 3D images of fragile but biologically important molecules inside protein nanocrystals.

Using the Linac Coherence Light Source (LCLS), a powerful at the SLAC National Accelerator Laboratory in Menlo Park, Calif., the scientists fired femtosecond (one quadrillionth of a second) bursts of light at a stream of tumbling molecules, obliterating them as they passed — but not before capturing otherwise illusive images of their crystalline structures.

“These laser pulses are so brief that we are able to outrun the radiation’s damaging effects,” said John C. H. Spence of Arizona State University, one of more than 70 international researchers from institutions including SLAC; DESY, the German Electron Synchrotron; and the Max-Planck Institute in Heidelberg, Germany.

“Using this so-called ‘diffract-then-destroy’ approach, our research team recorded about a hundred scattering patterns per second from protein nanocrystals,” said Spence. “This is an important step toward making movies of biomolecules at work.”

In traditional crystallography, a beam of X-rays first interacts with a crystal and then appears on a photodetector as diffraction spots of greater and lesser intensity. These patterns encode the density of electrons in the crystal, enabling scientists to determine the three-dimensional position of atoms, chemical bonds, and other information. T

o obtain this information, the crystal is frozen, to reduce radiation damage, and placed on a rotating mount and bombarded with X-rays as its orientation is changed. A scattering pattern is slowly built up and the 3D structure can eventually be deduced. But the freezing prevents observation of the molecules in their native liquid environment at room temperature.

How to capture 3D images of biomolecules

To obtain images of these molecules in the more natural state, the researchers sent the protein nanocrystals streaming in a single-file micron-sized droplet beam (rather like an ink-jet printer) in vacuum across the X-ray beam, in a method developed at Arizona State University.

Next they fired incredibly brief bursts of X-ray laser light, about 100 times each second, at the molecules in the droplet beam, and detected the scattered X-ray patterns from each particle before the intensity of the beam blasted them apart. The researchers were able to combine these millions of snapshots to build up 3D models of the molecules with atomic-scale resolution.

One particular molecule that was studied this way was Photosystem 1-ferredoxin, which is the chemical powerhouse that drives photosynthesis. The molecules for this experiment were made in the laboratory of Arizona State University researcher Petra Fromme.

Photosystem 1 harnesses sunlight to split water to make the oxygen we breathe, absorb carbon dioxide, and produce sugars, which maintains our biosphere. These molecules were studied “in action” by exciting them with a pulse of green laser light (to mimic the effect of sunlight falling on a leaf) a few microseconds before taking their X-ray snapshot.

Each snapshot then became one frame of a movie. By changing the delay between green pulse and X-ray pulse, the researchers could create a 3D movie of a biomolecule in action.

Other proteins

“Many other groups we are supporting now are applying the method to other proteins, such as enzymes, drug molecule targets, and imaging chemical reactions as they develop along the liquid jet,” said Spence. “The important thing was to get atomic-resolution snapshot images from nanocrystals at room temperature without radiation damage.”

An overview and early results of this new imaging technique will be presented at the 2012 meeting of the American Crystallographic Association (ACA), which takes place July 28 — Aug. 1 in Boston, Mass.

A complete listing of the collaborating research institutions follows:

Center for Free-Electron Laser Science, DESY, Hamburg, Germany

Photon Science, DESY, Hamburg, Germany

Department of Chemistry and Biochemistry, Arizona State University, Tempe

Comments (5)

Actual movies of chemical reactions!!!!!! When James Cameron made Pandora, he created a new green screen tech. They would film the actors performing the plot,( xraycrystalografy ) then after the actors left, he would carry around an iPad like device , of his own creation, and depending on where he was on the stage, and the direction that the tablet was “looking” he could see a crude animation of how it would look, after CGG created the background. In a very similar manner, the scientists will be able to view chemical interactions. Very awesome indeed!!!!

I’m ususally very happy with Google results, but not this time. The first article to come up for the question only mentioned that red light was absorbed, but it didn’t give the frequency. The article was very certain that green light is reflected.

If you’re looking for specific or in-depth information, try Wikipedia. The article on chlorophyll shows several frequency absorption graphs. As for your comment below, the peak absorption wavelength of chlorophyll is roughly 680nm, although it is able to absorb it (and, in a plant, utilize it for photosynthesis) in other wavelengths around the red and blue frequencies. It should be noted that chlorophyll is nearly as good absorbing light around the 420nm wavelength (blue).

That puzzled me too, Jamie. When I studied botony I was taught that chlorophyll absorbed a very specific frequency of red light. Something like 470 Angstrom units. But my memory is fuzzy at the age of 60. Let me go look it up.

I guess my only question would be, why would they utilize green light to mimic the effect of sunlight when this is the color that is reflected back by the chlorophyl, which is of course why plants are green in color?